As schematically illustrated in FIG. 1, a foam dispenser 1 generally comprises a container 2 having a mouth piece 3 at its top. The container 2 contains a substance 4, which turns into a foam on release. An example is soap, or shaving foam. In normal use, the container 2 is standing upright, and foam is dispensed from the mouth piece 3 by a user pressing the mouth piece down.
For achieving the dispensing action, the dispenser 1 comprises a pump mechanism actuated by the mouth piece. The combination of mouth piece and pump mechanism is typically implemented as a unit that is provided with a screw connector or a snap connector, for being screwed or snapped on a cylindrical neck portion of the container.
In prior art, the pump mechanism comprises a buffer chamber, on the one hand coupled to the interior of the container, on the other hand coupled to the mouth piece. On the down stroke of the mouth piece, a first flow path between the interior of the container and the buffer chamber is closed, a second flow path between the buffer chamber and the mouth piece is opened, the pressure within the buffer chamber is increased, and substance is pressed from the buffer chamber towards the mouth piece. On the up stroke of the mouth piece, the first flow path is opened, the second flow path is closed, the pressure within the buffer chamber is lowered, and substance is sucked from the container into the buffer chamber.